This invention relates to a secure data processing terminal, and more particularly to such a terminal utilizing a cathode ray tube (CRT) display in which information-bearing electromagnetic radiation is suppressed.
Almost all electronic equipment emits various amounts of electromagnetic energy by radiation of electric and magnetic fields and by conduction along power leads and signal lines. This type of self-generated electromagnetic radiation in undesirable, as it interferes with the functioning of the equipment as well as other equipments which are close proximity thereto In the case of communications and data processing equipment, the information being processed can be extracted from self-generated undesirable radiation In security applications, and in military applications where the data being processed may be classified, the undesired radiation could compromise the security of the systems. For commercial appications, unscrupulous competitors might find a way to utilize the extraneous radiations from the display terminals to obtain proprietary information.
In the past, the securing of terminals utilizing a CRT display has involved completely enclosing terminal in a shielded container, and using specially plated conductive glass to cover the cathode ray tube display of the terminal. This brute force approach to the problem is not only bulky and expensive, but also restricts the visibility of the display. The use of a piece of shielded glass in front of the CRT viewing area was apparently dictated by the belief that a large amount of radiation was generated directly from the face of CRT. However, the applicant has discovered that this is not the case, and that a secure terminal can be provided without the necessity of a shielded glass over the face of the tube, and without the necessity of enclosing the entire display unit within the confines of a shield. It has been discovered that the principal sources of unwanted radiation occur at the socket and neck of the CRT and in the video circuits leading thereto.
Accordingly, it is an object of this invention to provide a new and improved data processing terminal having a cathode ray tube display in which unwanted radiation containing the information being processed by the terminal is suppressed.
Another object of this invention is to provide a new and improved radiation-free data processing terminal utilizing a cathode ray tube display which eliminates the need for totally encasing the entire data processing terminal in a shielded enclosure utilizing a piece of shielded glass in front of the CRT viewing area of the terminal.
A further object of this invention is to provide a secure data-processing terminal which suppresses unwanted radiation with a simple, straight-forward approach readily adaptable to existing terminals.